Method for manufacturing titanium trichloride solution and device for manufacturing titanium trichloride solution

ABSTRACT

A method for manufacturing a titanium trichloride solution according to an embodiment of the present invention is a method for manufacturing a titanium trichloride solution, the method including reducing titanium tetrachloride in an electrolyte solution by using an ion-exchange electrolytic reduction method. In the method, an aqueous solution containing sulfate ions is used as an electrolyte solution on the anode side. A device for manufacturing a titanium trichloride solution according to another embodiment of the present invention is a device for manufacturing a titanium trichloride solution by electrolytic reduction of titanium tetrachloride in an aqueous solution. The device includes an anode chamber that stores an anode electrolyte solution, a cathode chamber that is separated from the anode chamber by an ion-exchange membrane and that stores the titanium tetrachloride solution, an anode immersed in the anode electrolyte solution in the anode chamber, and a cathode immersed in the titanium tetrachloride solution in the cathode chamber. In the device, the anode electrolyte solution contains sulfate ions.

TECHNICAL FIELD

The present invention relates to a method for manufacturing a titanium trichloride solution and a device for manufacturing a titanium trichloride solution.

The present application claims priority from Japanese Patent Application No. 2015-200520 filed on Oct. 8, 2015, and the entire contents of the Japanese patent application are incorporated herein by reference.

BACKGROUND ART

In a liquid-phase reduction method in which metal ions in an aqueous solution is reduced with a reducing agent to manufacture a metal powder, a titanium trichloride solution is used as the reducing agent. It is known that a titanium trichloride solution can be manufactured by subjecting a titanium tetrachloride solution to electrolytic reduction (refer to, for example, Japanese Unexamined Patent Application Publication No. 2012-255188).

In the method for manufacturing a titanium trichloride solution described in the patent application publication, an aqueous solution containing titanium tetrachloride, hydrochloric acid, and an oxidation inhibitor is used as an electrolyte solution on the cathode side, and a chloride ion-containing aqueous solution such as an aqueous ammonium chloride solution, an aqueous sodium chloride solution, or an aqueous titanium chloride solution is used as an electrolyte solution on the anode side.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No. 2012-255188

SUMMARY OF INVENTION

A method for manufacturing a titanium trichloride solution according to an embodiment of the present invention is a method for manufacturing a titanium trichloride solution, the method including reducing titanium tetrachloride in an electrolyte solution by using an ion-exchange electrolytic reduction method. In the method, an aqueous solution containing sulfate ions is used as an electrolyte solution on the anode side.

A device for manufacturing a titanium trichloride solution according to another embodiment of the present invention is a device for manufacturing a titanium trichloride solution by electrolytic reduction of titanium tetrachloride in an aqueous solution. The device includes an anode chamber that stores an anode electrolyte solution, a cathode chamber that is separated from the anode chamber by an ion-exchange membrane and that stores the titanium tetrachloride solution, an anode immersed in the anode electrolyte solution in the anode chamber, and a cathode immersed in the titanium tetrachloride solution in the cathode chamber. In the device, the anode electrolyte solution contains sulfate ions.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a schematic view illustrating a device for manufacturing a titanium trichloride solution according to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS Technical Problem

In the method for manufacturing a titanium trichloride solution, the method including using a chloride ion-containing aqueous solution as an electrolyte solution on the anode side, chloride ions may generate chlorine gas due to the anodic reaction and react with another solute component in the electrolyte solution to generate chloride gas. Accordingly, in the method for manufacturing titanium trichloride, it is usually necessary to suction and discharge the generated gas.

In order to reduce the cost for treating such chlorine-based gas, it is desirable to reduce the amount of chlorine-based gas generated in the manufacturing of a titanium trichloride solution.

The present invention has been made in view of the circumstances described above. An object of the present invention is to provide a method for manufacturing a titanium trichloride solution and a device for manufacturing a titanium trichloride solution, in which the amount of chlorine-based gas generated can be reduced.

Advantageous Effects of the Present Disclosure

According to the method for manufacturing a titanium trichloride solution according to an embodiment of the present invention and the device for manufacturing a titanium trichloride solution according to another embodiment of the present invention, the amount of chlorine-based gas generated can be reduced.

Description of Embodiments of the Present Invention

A method for manufacturing a titanium trichloride solution according to an embodiment of the present invention is a method for manufacturing a titanium trichloride solution, the method including reducing titanium tetrachloride in an electrolyte solution by using an ion-exchange electrolytic reduction method. In the method, an aqueous solution containing sulfate ions is used as an electrolyte solution on the anode side. The term “ion-exchange electrolytic reduction method” refers to an electrolytic reduction method in which electrolysis is conducted in a state where an electrolyte solution on the anode side and an electrolyte solution on the cathode side are divided by an ion-exchange membrane.

According to the method for manufacturing a titanium trichloride solution, by using an aqueous solution containing sulfate ions as the electrolyte solution on the anode side, a chloride ion concentration of the electrolyte solution on the anode side is suppressed to be low to prevent chloride ions in the electrolyte solution on the anode side from unnecessarily reacting with the electrolyte solution and another substance in the air, and thus the amount of chlorine-based gas generated can be reduced.

A molar concentration of the sulfate ions in the electrolyte solution on the anode side is preferably equal to or more than a total molar concentration of other anions. When the molar concentration of the sulfate ions in the electrolyte solution on the anode side is equal to or more than the total molar concentration of other anions, generation of chlorine-based gas can be more reliably prevented.

The ion-exchange membrane is preferably a cation-exchange membrane. When the ion-exchange membrane is a cation-exchange membrane, it is possible to prevent chloride ions in the electrolyte solution on the cathode side from transferring to the anode side. Thus, generation of a chlorine-based gas can be further suppressed.

A total molar concentration of metal ions in the electrolyte solution on the anode side is preferably 1/10 or less of the molar concentration of the sulfate ions. When the total molar concentration of metal ions in the electrolyte solution on the anode side is equal to or less than the upper limit, the amount of metal ions in carriers that transfer from the anode side to the cathode side is decreased, and a decrease in the reaction efficiency of the cathode can be suppressed.

The ion-exchange membrane may be an anion-exchange membrane. When the ion-exchange membrane is an anion-exchange membrane, an electrolysis vessel used in an existing method for manufacturing a titanium trichloride solution can be used, and thus the equipment cost can be reduced.

The method preferably includes a step of adding an oxidation inhibitor to the electrolyte solution on the cathode side. When the method includes a step of adding an oxidation inhibitor to the electrolyte solution on the cathode side, oxidation of trivalent titanium ions produced by the cathodic reaction is suppressed, and a titanium trichloride solution can be relatively efficiently manufactured.

A carboxylic acid having two or more carboxyl groups or a salt of the carboxylic acid is preferably used as the oxidation inhibitor. The use of a carboxylic acid having two or more carboxyl groups or a salt of the carboxylic acid as the oxidation inhibitor more effectively suppresses oxidation of trivalent titanium ions and enables a titanium trichloride solution having a relatively good storage property to be manufactured.

A device for manufacturing a titanium trichloride solution according to another embodiment of the present invention is a device for manufacturing a titanium trichloride solution by electrolytic reduction of titanium tetrachloride in an aqueous solution. The device includes an anode chamber that stores an anode electrolyte solution, a cathode chamber that is separated from the anode chamber by an ion-exchange membrane and that stores the titanium tetrachloride solution, an anode immersed in the anode electrolyte solution in the anode chamber, and a cathode immersed in the titanium tetrachloride solution in the cathode chamber. In the device, the anode electrolyte solution contains sulfate ions.

According to the device for manufacturing a titanium trichloride solution, since the anode electrolyte solution contains sulfate ions, the chloride ion concentration of the electrolyte solution on the anode side is suppressed to be low to prevent chlorine and chlorides from being unnecessarily produced, and thus the amount of chlorine-based gas generated can be reduced.

Details of Embodiment of the Present Invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawing.

A device for manufacturing a titanium trichloride solution illustrated in FIG. 1 is used for manufacturing a titanium trichloride solution (TiCl₃) by subjecting titanium tetrachloride (TiCl₄) in an aqueous solution to electrolytic reduction.

The device for manufacturing a titanium trichloride solution includes an electrolysis vessel 1 and preferably further includes a power supply 2 that applies a voltage to the electrolysis vessel 1.

<Electrolysis Vessel>

The electrolysis vessel 1 includes an anode chamber 11 that stores an electrolyte solution on the anode side (hereinafter, may be referred to as an “anode electrolyte solution”), a cathode chamber 13 that is separated from the anode chamber 11 by an ion-exchange membrane 12 and that stores a titanium tetrachloride solution serving as an electrolyte solution on the cathode side (hereinafter, may be referred to as a “cathode electrolyte solution”), an anode 14 immersed in the anode electrolyte solution in the anode chamber 11, and a cathode 15 immersed in the titanium tetrachloride solution in the cathode chamber 13. The power supply 2 applies a direct-current voltage between the anode 14 and the cathode 15.

(Anode Chamber)

The anode chamber 11 is one of two spaces formed by dividing the inner space of the electrolysis vessel 1 by the ion-exchange membrane 12, the one space including the anode 14 therein. In other words, the anode chamber 11 is adjacent to the cathode chamber 13 with the ion-exchange membrane 12 therebetween. The anode chamber 11 stores, as the anode electrolyte solution, an aqueous solution containing sulfate ions, as described in detail later.

(Ion-Exchange Membrane)

The ion-exchange membrane 12 is a membrane that divides the inner space of the electrolysis vessel 1 into the anode chamber 11 and the cathode chamber 13 and allows cations or anions to selectively pass. That is, ions capable of passing through the ion-exchange membrane 12 can transfer between the anode chamber 11 and the cathode chamber 13. The ions passing through the ion-exchange membrane 12 function as carriers that transfer electric charges between the anode 14 and the cathode 15 and enable an electric current to flow between the anode 14 and the cathode 15.

The ion-exchange membrane 12 is not particularly limited, and a known cation-exchange membrane or a known anion-exchange membrane can be used as the ion-exchange membrane 12. When a cation-exchange membrane, which allows cations to selectively pass, is used as the ion-exchange membrane 12, for example, a hydrocarbon-based ion-exchange membrane or a polymer perfluorocarbon-based ion-exchange membrane can be used. An example of the hydrocarbon-based ion-exchange membrane that can be used is an ion-exchange membrane obtained by introducing a cation-exchange group into a hydrocarbon-based polymer such as a styrene-divinylbenzene copolymer. An example of the polymer perfluorocarbon-based ion-exchange membrane that can be used is an ion-exchange membrane having a perfluoroalkylene group as a main chain backbone, perfluorovinyl ether as a part of a side chain thereof, and a cation-exchange group introduced in an end of the side chain. Examples of the cation-exchange group include a sulfonic acid group and a carboxylic acid group.

When a cation-exchange membrane is used as the ion-exchange membrane 12 in this manner, the device for manufacturing a titanium trichloride solution applies an electric current between the anode 14 and the cathode 15 while hydrogen ions (H⁺) produced by electrolysis of water in the anode electrolyte solution function as carriers, to thereby reduce tetravalent titanium ions in the cathode electrolyte solution. This configuration prevents chloride ions (Cl⁻) in the cathode electrolyte solution from transferring into the anode electrolyte solution and can more effectively prevent the chloride ions from being provided to the anodic reaction and generating chlorine gas.

When an anion-exchange membrane, which allows anions to selectively pass, is used as the ion-exchange membrane 12, it is possible to use, for example, a hydrocarbon-based ion-exchange membrane including a styrene-divinylbenzene copolymer as a main chain backbone and having a quaternary ammonium group at an end thereof.

When an anion-exchange membrane is used as the ion-exchange membrane 12 in this manner, chloride ions in the cathode electrolyte solution become carriers that transfer electric charges and transfer into the anode electrolyte solution, which enables an electric current to flow between the anode 14 and the cathode 15. In this case, since the permeability of the carriers can be made high, the power consumption can be reduced. When an anion-exchange membrane is used as the ion-exchange membrane 12, chloride ions, which have become carriers, generate chlorine gas due to the anodic reaction. However, since the anode electrolyte solution contains sulfate ions (SO₄ ²⁻), it is possible to suppress a reaction of chloride ions beyond the need for the anodic reaction. Specifically, it is possible to prevent chloride ions in the anode electrolyte solution from reacting with nitrogen in the air and producing, for example, nitrogen trichloride.

An advantage achieved by using an anion-exchange membrane as the ion-exchange membrane 12 is a reduction in the equipment cost because an ion-exchange electrolysis device that has hitherto been relatively widely used can be used without modification.

The lower limit of the average thickness of the ion-exchange membrane 12 is preferably 0.02 mm and more preferably 0.05 mm. The upper limit of the average thickness of the ion-exchange membrane 12 is preferably 2 mm and more preferably 0.5 mm. When the average thickness of the ion-exchange membrane 12 is less than the lower limit, sufficient strength of the ion-exchange membrane 12 cannot be ensured, and ion selectivity (ion-exchange capacity) may decrease. In contrast, when the average thickness of the ion-exchange membrane 12 exceeds the upper limit, a decrease in the permeability of ions causes a decrease in the current density, and the reaction may become inefficient.

The anode chamber 11 is separated from the cathode chamber 13 with the ion-exchange membrane 12 therebetween. That is, ions capable of passing through the ion-exchange membrane 12 can transfer between the electrolyte solution on the anode side, the electrolyte solution being stored in the anode chamber 11, and the electrolyte solution on the cathode side, the electrolyte solution being stored in the cathode chamber 13.

(Cathode Chamber)

The cathode chamber 13 has a supply port 16 and a discharge port 17. The supply port 16 is used for supplying a titanium tetrachloride solution and disposed on the lower side of the cathode chamber 13. The discharge port 17 is used for discharging a titanium trichloride solution and disposed on the upper side of the cathode chamber 13. That is, a titanium trichloride solution can be continuously manufactured in the electrolysis vessel 1 by continuously supplying a titanium tetrachloride solution.

Herein, the term “titanium tetrachloride solution” covers a titanium solution supplied to the cathode chamber 13 and a titanium solution present in the cathode chamber 13 (solution in which titanium tetrachloride and titanium trichloride coexist). The term “titanium trichloride solution” refers to a solution containing trivalent titanium ions, the solution being discharged from the discharge port 17 of the electrolysis vessel 1 (cathode chamber 13).

<Anode>

The anode 14 takes out electrons (e) from the anode electrolyte solution. Examples of the reaction in which electrons are taken out from the anode electrolyte solution include a reaction in which an electron is removed from an anion in the anode electrolyte solution to oxidize the anion and a reaction in which water in the anode electrolyte solution is subjected to electrolysis to produce hydrogen ions and oxygen (O₂).

The anode 14 is formed to have, for example, a plate shape. The anode 14 is preferably formed as a porous body containing a conductive substance. Known electrode materials can be used as the conductive substance. Examples of the conductive substance include titanium, conductive carbon, nickel, and iridium oxide. Of these, titanium is preferred. An anode obtained by covering a surface of a conductive substance with a metal having high corrosion resistance, such as platinum, gold, or rhodium may also be used as the anode 14.

The anode 14 formed as a porous body can promote the anodic reaction, and consequently, promote the cathodic reaction to efficiently produce titanium trichloride.

The porous body can be formed by a known method. For example, the porous body can be formed by a method in which a urethane foam or the like to which conductivity has been imparted is subjected to plating and then fired, a method in which a metal powder is caused to adhere to a urethane foam or the like coated with an adhesive and then fired, and a method in which a mold is filled with metallic fibers and the resulting molded body is then sintered.

The porosity of the porous body is preferably 30% or more and 99% or less in order to increase the contact area with the anode electrolyte solution to promote the anodic reaction. Herein, the term “porosity” refers to a value measured in accordance with JIS-Z2501 (2000) “Sintered metal materials-Determination of density, oil content, and open porosity”.

The lower limit of the average thickness of the anode 14 is preferably 0.2 mm and more preferably 0.5 mm. The upper limit of the average thickness of the anode 14 is preferably 5 mm and more preferably 2 mm. When the average thickness of the anode 14 is less than the lower limit, the anode 14 has a high electrical resistance, and the amount of electrons supplied to the cathode 15 may decrease. In contrast, when the average thickness of the anode 14 exceeds the upper limit, the moving distance of molecules in the anode 14 increases, and the efficiency of the anodic reaction may decrease.

<Cathode>

The cathode 15 reduces a tetravalent titanium ion (Ti⁴⁺) to a trivalent titanium ion (Ti³⁺), specifically, adds an electron to a tetravalent titanium ion. The cathode 15 is formed to have, for example, a plate shape. The cathode 15 is arranged such that a lower end thereof is located in front of the supply port 16 of the electrolysis vessel 1. By arranging the cathode 15 in this manner, a titanium tetrachloride solution is supplied from the supply port 16 toward the lower end of the cathode 15. On the other hand, the discharge port 17 is arranged above the supply port 16. Therefore, in the cathode chamber 13, a flow from the lower end of the cathode 15 toward the upper end thereof is generated along the surface of the cathode 15. Thus, titanium trichloride produced by the cathodic reaction can be efficiently introduced to the discharge port 17.

The cathode 15 is not particularly limited as long as the cathode 15 has electrical conductivity and corrosion resistance to hydrochloric acid. A conductive metal such as iron, an alloy, graphite, or the like is used as the cathode 15. A cathode obtained by covering a surface of a conductive metal with a metal having high corrosion resistance, such as platinum, gold, or rhodium may also be used as the cathode 15.

In the case where the ion-exchange membrane 12 is a cation-exchange membrane, the device for manufacturing a titanium trichloride solution may include a catalyst layer (not shown) that is arranged between the ion-exchange membrane 12 and the anode 14 and that increases the reaction rate of electrolysis of water. This catalyst layer is preferably arranged so as to be in contact with both the anode 14 and the ion-exchange membrane 12.

When the catalyst layer is fixed between the anode 14 and the ion-exchange membrane 12 in this manner, water is efficiently supplied to the catalyst layer, and hydrogen ions produced by the anodic reaction permeate through the ion-exchange membrane 12 efficiently. Accordingly, electrons are efficiently received from water in the anode 14, and the electrons can be supplied to the cathode 15, and thus titanium tetrachloride can be efficiently reduced. On the other hand, since chloride ions produced by the cathodic reaction and hydrogen ions coexist in the cathode chamber 13, oxidation degradation of titanium trichloride produced by the cathodic reaction can be effectively suppressed.

The catalyst layer can be formed by, for example, impregnating the anode 14 or the ion-exchange membrane 12 with a solution containing ions for a catalyst, subsequently stacking the anode 14 and the ion-exchange membrane 12, and reducing the ions for the catalyst. Examples of the material constituting the catalyst layer include noble metals such as platinum, rhodium, and iridium oxide.

<Power Supply>

The power supply 2 applies a direct-current voltage between the anode 14 and the cathode 15. The power supply 2 is not particularly limited as long as the power supply 2 can apply a predetermined voltage, and a known direct-current power supply unit can be used.

<Anode Electrolyte Solution>

As described above, an aqueous solution containing sulfate ions is stored as an anode electrolyte solution in the anode chamber 11. An aqueous solution of a sulfate such as sodium sulfate or calcium sulfate besides sulfuric acid can be used as the aqueous solution containing sulfate ions. The anode electrolyte solution may contain, for example, an additive such as an osmotic pressure-adjusting agent for adjusting the difference in osmotic pressure between the anode chamber 11 and the cathode chamber 13.

The lower limit of the molar concentration of sulfate ions in the anode electrolyte solution is preferably 0.05 mol/L, more preferably 0.1 mol/L, and still more preferably 0.2 mol/L. The upper limit of the molar concentration of sulfate ions in the anode electrolyte solution is preferably 2 mol/L, more preferably 1 mol/L, and still more preferably 0.7 mol/L. When the molar concentration of sulfate ions in the anode electrolyte solution is less than the lower limit, the anodic reaction may not be sufficiently promoted, or the generation of chlorine gas may not be sufficiently suppressed. In contrast, when the molar concentration of sulfate ions in the anode electrolyte solution exceeds the upper limit, the osmotic pressure of the anode electrolyte solution becomes excessively high. As a result, the transfer of carriers is suppressed, and the reaction efficiency may decrease.

The anode electrolyte solution preferably has a low concentration of anions other than sulfate ions. The lower limit of a ratio of the molar concentration of sulfate ions to a total molar concentration of other anions in the anode electrolyte solution is preferably 1, more preferably 10, still more preferably 20, and even still more preferably 50. On the other hand, the upper limit of the ratio of the molar concentration of sulfate ions to the total molar concentration of other anions in the anode electrolyte solution is not particularly limited. When the ratio of the molar concentration of sulfate ions to the total molar concentration of other anions in the anode electrolyte solution is less than the lower limit, the production of chlorine gas due to the anodic reaction may not be sufficiently suppressed, or an undesirable reaction may occur due to the other anions.

In the case where the ion-exchange membrane 12 is a cation-exchange membrane, metal ions in the anode electrolyte solution can transfer into the cathode electrolyte solution through the ion-exchange membrane 12. Accordingly, in the case where the ion-exchange membrane 12 is a cation-exchange membrane, a total concentration of metal ions in the anode electrolyte solution is preferably as low as possible. The upper limit of the total molar concentration of metal ions in the anode electrolyte solution is preferably 1/10, more preferably 1/20, and still more preferably 1/50 of the molar concentration of sulfate ions. When the total molar concentration of metal ions in the anode electrolyte solution exceeds the upper limit, the metal ions in the anode electrolyte solution transfer into the cathode electrolyte solution and are reduced by consuming electrons supplied from the cathode, which may result in inhibition of reduction of titanium ions, or the metal ions are mixed as impurities in the resulting titanium trichloride solution, which may result in degradation of the quality of the solution.

Examples of the osmotic pressure-adjusting agent that may be contained in the anode electrolyte solution include citric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, tartaric acid, malic acid, fumaric acid, maleic acid, itaconic acid, phthalic acid, isophthalic acid, terephthalic acid, and salts thereof. These may be used alone or in combination of two or more thereof. The amount of osmotic pressure-adjusting agent added is determined in accordance with, for example, a target difference in osmotic pressure and the type of osmotic pressure-adjusting agent used. The amount of osmotic pressure-adjusting agent added is, for example, more than 0 mol/L and 2 mol/L or less. When the amount of osmotic pressure-adjusting agent added exceeds the upper limit, ions other than titanium ions are increased in the cathode electrolyte solution, and reduction of titanium ions may be inhibited.

<Cathode Electrolyte Solution>

As described above, a titanium tetrachloride solution that produces a titanium trichloride solution by being subjected to electrolytic reduction is supplied as a cathode electrolyte solution to the cathode chamber 13. This cathode electrolyte solution preferably contains hydrochloric acid. An oxidation inhibitor that inhibits oxidation of a trivalent titanium ion produced by electrolytic reduction to a tetravalent titanium ion is preferably added to the titanium tetrachloride solution before electrolysis, the titanium tetrachloride solution being supplied to the cathode chamber 13. The flow rate of the titanium tetrachloride solution supplied to the electrolysis vessel 1 (cathode chamber 13) is set so that, for example, a concentration of trivalent titanium ions in the discharge port 17 preferably becomes 90% by mole or more and more preferably nearly 100% by mole in terms of a ratio relative to a total amount of trivalent titanium ions and tetravalent titanium ions.

The lower limit of the concentration of titanium ions (total concentration of trivalent titanium ions and tetravalent titanium ions) in the cathode electrolyte solution is preferably 0.05 mol/L, more preferably 0.1 mol/L, and still more preferably 0.2 mol/L. The upper limit of the concentration of titanium ions in the cathode electrolyte solution is preferably 2 mol/L, more preferably 1 mol/L, and still more preferably 0.7 mol/L. When the concentration of titanium ions in the cathode electrolyte solution is less than the lower limit, the cathodic reaction may not be sufficiently promoted, or the concentration of the resulting titanium trichloride solution may be insufficient. In contrast, when the concentration of titanium ions in the cathode electrolyte solution exceeds the upper limit, the amount of unreacted titanium tetrachloride increases, and the resulting titanium trichloride solution may have an insufficient quality.

The upper limit of the concentration of hydrochloric acid is not particularly limited but is preferably 2 mol/L. The lower limit of the concentration of hydrochloric acid is preferably 0.5 mol/L and more preferably 1.5 mol/L. When the titanium trichloride solution has a hydrochloric acid concentration within the above range, oxidation degradation of trivalent titanium ions can be more effectively suppressed, and the titanium trichloride solution has a good storage property.

The oxidation inhibitor is preferably a carboxylic acid having two or more carboxyl groups or a salt of the carboxylic acid. The carboxylic acid or the carboxyl acid salt is coordinated to a trivalent titanium ion to form a titanium complex. As a result, the frequency in which the trivalent titanium ion and oxygen become close to each other is decreased to effectively suppress oxidation of the trivalent titanium ion.

Examples of the oxidation inhibitor include citric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, tartaric acid, malic acid, fumaric acid, maleic acid, itaconic acid, phthalic acid, isophthalic acid, terephthalic acid, and salts thereof. These may be used alone or in combination of two or more thereof.

The lower limit of the molar concentration of the oxidation inhibitor in the titanium tetrachloride solution supplied to the cathode chamber 13 (cathode electrolyte solution before electrolysis) is preferably 0.1 times and more preferably 0.15 times the total molar concentration of trivalent titanium ions and tetravalent titanium ions in the cathode electrolyte solution. The upper limit of the molar concentration of the oxidation inhibitor in the titanium tetrachloride solution supplied to the cathode chamber 13 is preferably 2 times and more preferably 1.5 times the total molar concentration of the titanium ions. When the molar concentration of the oxidation inhibitor in the titanium tetrachloride solution supplied to the cathode chamber 13 is less than the lower limit, oxidation of trivalent titanium ions may not be sufficiently suppressed. In contrast, when the molar concentration of the oxidation inhibitor in the titanium tetrachloride solution supplied to the cathode chamber 13 exceeds the upper limit, the reduction of tetravalent titanium ions and the transfer of carriers between the anode chamber 11 and the cathode chamber 13 may be inhibited.

An oxidation inhibitor is preferably further added to the titanium trichloride solution produced in the cathode chamber 13 (cathode electrolyte solution after electrolysis). In particular, in the case where an anion-exchange membrane is used as the ion-exchange membrane 12, chloride ions in the cathode electrolyte solution transfer into the anode chamber 11, which tends to decrease the function of suppressing production of titanium oxide due to oxidation of trivalent titanium ions in the cathode electrolyte solution, the function being achieved by the chloride ions. Accordingly, it is more effective to add an oxidation inhibitor to the cathode electrolyte solution after electrolysis reaction so that the concentration of trivalent titanium ions can be maintained.

The lower limit of the molar concentration of the oxidation inhibitor in the titanium trichloride solution to which the oxidation inhibitor is added after electrolysis is preferably 0.3 times and more preferably 0.4 times the total molar concentration of trivalent titanium ions and tetravalent titanium ions in the cathode electrolyte solution. The upper limit of the molar concentration of the oxidation inhibitor in the titanium trichloride solution is preferably 5 times and more preferably 2 times the total molar concentration of the titanium ions. When the molar concentration of the oxidation inhibitor in the titanium trichloride solution is less than the lower limit, oxidation of trivalent titanium ions may not be sufficiently suppressed. In contrast, when the molar concentration of the oxidation inhibitor in the titanium trichloride solution exceeds the upper limit, the cost may be unnecessarily increased, or the use of the resulting titanium trichloride solution may be limited.

[Method for Manufacturing Titanium Trichloride]

Next, a description will be given of a method for manufacturing a titanium trichloride solution according to another embodiment of the present invention, the method being capable of being carried out by using the device for manufacturing a titanium trichloride solution.

The method for manufacturing a titanium trichloride solution is a method for manufacturing a titanium trichloride solution, the method including reducing titanium tetrachloride in an electrolyte solution by using an ion-exchange electrolytic reduction method.

In the method for manufacturing a titanium trichloride solution, an aqueous solution containing sulfate ions is used as an electrolyte solution on the anode 14 side, as described in the device for manufacturing a titanium trichloride solution. Specifically, in the method for manufacturing titanium trichloride, an aqueous solution containing sulfate ions is stored in the anode chamber 11, a titanium tetrachloride solution is stored in the cathode chamber 13, and a voltage is applied between the anode 14 and the cathode 15, thereby subjecting titanium tetrachloride in the cathode chamber 13 to electrolytic reduction to manufacture a titanium trichloride solution.

<Application of Voltage>

The voltage is applied by the power supply 2. The application voltage is preferably 3 V or more and 10 V or less and is typically 5 V. The current density is preferably 20 mA/cm² or more and 40 mA/cm² or less and is typically 30 mA/cm².

The method for manufacturing a titanium trichloride solution preferably includes a step of adding an oxidation inhibitor to the cathode chamber 13. Specifically, in the method for manufacturing a titanium trichloride solution, an oxidation inhibitor is preferably added so as to have the molar concentration described above preferably to the cathode electrolyte solution before electrolysis or the cathode electrolyte solution after electrolysis and more preferably to the cathode electrolyte solution before electrolysis and after electrolysis. This step can improve storage stability of the titanium trichloride solution to be produced.

<Advantages>

According to the device for manufacturing a titanium trichloride solution and the method for manufacturing a titanium trichloride solution, by using an aqueous solution containing sulfate ions as an electrolyte solution on the anode 14 side, the chloride ion concentration of the electrolyte solution on the anode 14 side is suppressed to be low to prevent chlorine and chlorides from being unnecessarily produced, and thus the amount of chlorine-based gas generated can be reduced.

Other Embodiments

It is to be understood that the embodiments disclosed herein are only illustrative and are not restrictive in all respects. The scope of the present invention is not limited to the configurations of the embodiments and is defined by the claims described below. The scope of the present invention is intended to cover all the modifications within the meaning and scope of the claims and their equivalents.

In the device for manufacturing a titanium trichloride solution, the anode and the cathode may each have a gas passage through which gas produced in the electrolytic reduction reaction permeates.

The device for manufacturing a titanium trichloride solution may not include a power supply unit, and a voltage may be applied from the outside.

In the above embodiments, a description has been made of a case where a titanium tetrachloride solution is continuously supplied to the electrolysis vessel. Alternatively, a titanium trichloride solution may be manufactured from a titanium tetrachloride solution in a batch process.

Examples

The present invention will now be described in detail by using Examples. The description of Examples does not limit the interpretation of the present invention.

Trial manufacture examples 1 to 5 of titanium trichloride solutions were manufactured under different manufacturing conditions by using a manufacturing device corresponding to the device for manufacturing a titanium trichloride solution illustrated in FIG. 1. The device for manufacturing a titanium trichloride solution was installed in a hermetically sealed space so as to check a change in the chlorine gas concentration in the space.

(Trial Manufacture Example 1)

A titanium trichloride solution was manufactured by conducting electrolytic reduction by using, as an ion-exchange membrane, an anion-exchange membrane; as a cathode electrolyte solution, an aqueous solution containing 0.4 mol/L of titanium tetrachloride, 1.0 mol/L of hydrochloric acid, and 0.08 mol/L of trisodium citrate serving as an oxidation inhibitor; and, as an anode electrolyte solution, a 0.4 mol/L aqueous solution of sodium sulfate. To the cathode electrolyte solution immediately after the electrolytic reduction, trisodium citrate was further added as an oxidation inhibitor in an amount of 0.2 mole per 1 L of the cathode electrolyte solution. Thus, a trial manufacture example 1 of a titanium trichloride solution was prepared.

(Trial Manufacture Example 2)

A trial manufacture example 2 of a titanium trichloride solution was prepared under the same conditions as in the trial manufacture example 1 except that 0.4 mol/L sulfuric acid that did not contain metal ions was used as the anode electrolyte solution, and a cation-exchange membrane was used as the ion-exchange membrane.

(Trial Manufacture Example 3)

A trial manufacture example 3 of a titanium trichloride solution was prepared under the same conditions as in the trial manufacture example 1 except that the amount of trisodium citrate added immediately after the electrolytic reduction was 0.1 mole per 1 L of the cathode electrolyte solution.

(Trial Manufacture Example 4)

A trial manufacture example 4 of a titanium trichloride solution was prepared under the same conditions as in the trial manufacture example 1 except that trisodium citrate was not added after the electrolytic reduction.

(Trial Manufacture Example 5)

A trial manufacture example 5 of a titanium trichloride solution was prepared under the same conditions as in the trial manufacture example 1 except that 0.4 mol/L hydrochloric acid was used as the anode electrolyte solution.

(Chlorine Gas Concentration)

Immediately before the end of the electrolytic reduction in the manufacturing of the trial manufacture examples 1 to 5 of the titanium trichloride solutions, the chlorine concentration in the hermetically sealed space in which the device for manufacturing a titanium trichloride solution was installed was measured by using a portable gas detector “GasAlert Extreme GAXT-C-DL” available from JIKCO Co, Ltd.

(Storage Test)

Each of the trial manufacture examples 1 to 5 of the titanium trichloride solutions was stored for 3,600 hours, and trivalent titanium ion concentrations before and after the storage were measured by redox titration using a cerium(IV) sulfate solution in accordance with JIS-K0050 (2011). A ratio of the trivalent titanium ion concentration after storage to the trivalent titanium ion concentration immediately after manufacturing (the ratio being shown as a titanium ion concentration ratio after storage in Table 1) was calculated. In addition, the state of the titanium trichloride solution after storage was visually observed to examine whether or not a precipitate of titanium oxide (TiO₂) was produced.

Table 1 below summarizes the manufacturing conditions of the trial manufacture examples 1 to 5 of the titanium trichloride solutions, the measurement results of the chlorine gas concentration, and the results of the storage test. In the table, the expression “>500 ppm” in the chlorine gas concentration at the end of electrolysis means that the chlorine gas concentration exceeded 500 ppm, which was the upper detection limit of the gas detector used.

TABLE 1 Trial manufacture example No. 1 No. 2 No. 3 No. 4 No. 5 Cathode electrolyte solution Titanium tetrachloride Titanium tetrachloride Titanium tetrachloride Titanium tetrachloride Titanium tetrachloride 0.4 mol/L 0.4 mol/L 0.4 mol/L 0.4 mol/L 0.4 mol/L Hydrochloric acid Hydrochloric acid Hydrochloric acid Hydrochloric acid Hydrochloric acid 1.0 mol/L 1.0 mol/L 1.0 mol/L 1.0 mol/L 1.0 mol/L Trisodim citrate Trisodium citrate Trisodium citrate Trisodium citrate Trisodium citrate 0.08 mol/L 0.08 mol/L 0.08 mol/L 0.08 mol/L 0.08 mol/L Anode electrolyte solution Sodium sulfate Sulfuric acid Sodium sulfate Sodium sulfate Hydrochloric acid 0.4 mol/L 0.4 mol/L 0.4 mol/L 0.4 mol/L 0.4 mol/L Ion-exchange membrane Anion-exchange Cation-exchange Anion-exchange Anion-exchange Anion-exchange membrane membrane membrane membrane membrane Oxidation inhibitor Trisodium citrate Trisodium citrate Trisodium citrate None Trisodium citrate after electrolysis 0.2 mol/L 0.2 mol/L 0.1 mol/L 0.2 mol/L Chlorine gas concentration 300 ppm ≤1 ppm 300 ppm 300 ppm >500 ppm at end of electrolysis Titanium ion concentration 97% 97% 92% 90% 92% ratio after storage Precipitate after storage Not produced Not produced Not produced Produced Not produced

As shown in Table 1, in the trial manufacture examples 1 to 4, in which an aqueous solution containing sulfate ions was used as the anode electrolyte solution, the chlorine gas concentration at the end of the electrolysis was 300 ppm or less, showing that the generation of chlorine gas could be suppressed. In particular, in the trial manufacture example 2, in which a cation-exchange membrane was used as the ion-exchange membrane and sulfuric acid that did not contain metal ions was used as the anode electrolyte solution, the chlorine gas concentration at the end of the electrolysis was 1 ppm or less, showing that the amount of chlorine gas generated could be significantly reduced. Referring to the trial manufacture examples 1, 3, and 4, it was found that the addition of the oxidation inhibitor immediately after the electrolytic reduction prevents a precipitate of titanium oxide from generating in the titanium trichloride solution after storage and enables the trivalent titanium concentration to further increase.

REFERENCE SIGNS LIST

-   -   1 electrolysis vessel     -   2 power supply     -   11 anode chamber     -   12 ion-exchange membrane     -   13 cathode chamber     -   14 anode     -   15 cathode     -   16 supply port     -   17 discharge port 

1. A method for manufacturing a titanium trichloride solution, the method comprising reducing titanium tetrachloride in an electrolyte solution by using an ion-exchange electrolytic reduction method, wherein an aqueous solution containing sulfate ions is used as an electrolyte solution on the anode side.
 2. The method for manufacturing a titanium trichloride solution according to claim 1, wherein a molar concentration of the sulfate ions in the electrolyte solution on the anode side is equal to or more than a total molar concentration of other anions in the electrolyte solution on the anode side.
 3. The method for manufacturing a titanium trichloride solution according to claim 1, wherein a cation-exchange membrane is used as an ion-exchange membrane in the ion-exchange electrolytic reduction method.
 4. The method for manufacturing a titanium trichloride solution according to claim 3, wherein a total molar concentration of metal ions in the electrolyte solution on the anode side is 1/10 or less of the molar concentration of the sulfate ions.
 5. The method for manufacturing a titanium trichloride solution according to claim 1, wherein an anion-exchange membrane is used as an ion-exchange membrane in the ion-exchange electrolytic reduction method.
 6. The method for manufacturing a titanium trichloride solution according to claim 1, comprising a step of adding an oxidation inhibitor to the electrolyte solution on the cathode side.
 7. The method for manufacturing a titanium trichloride solution according to claim 6, wherein a carboxylic acid having two or more carboxyl groups or a salt of the carboxylic acid is used as the oxidation inhibitor.
 8. A device for manufacturing a titanium trichloride solution by electrolytic reduction of titanium tetrachloride in an aqueous solution, the device comprising an anode chamber that stores an anode electrolyte solution; a cathode chamber that is separated from the anode chamber by an ion-exchange membrane and that stores the titanium tetrachloride solution; an anode immersed in the anode electrolyte solution in the anode chamber; and a cathode immersed in the titanium tetrachloride solution in the cathode chamber, wherein the anode electrolyte solution contains sulfate ions. 